Shenandoah: Missing handshake after JDK-8263427

The test failed on Mar. 25 nightly.

# Internal Error (/home/jenkins/workspace/nightly/jdk-jdk/src/hotspot/share/classfile/javaClasses.cpp:745), pid=20943, tid=21063
# assert(java_string->klass() == vmClasses::String_klass()) failed: must be java_string
#
# JRE version: OpenJDK Runtime Environment (17.0) (fastdebug build 17-internal+0-adhoc.jenkins.jdk-jdk)
# Java VM: OpenJDK 64-Bit Server VM (fastdebug 17-internal+0-adhoc.jenkins.jdk-jdk, mixed mode, sharing, tiered, compressed oops, compressed class ptrs, shenandoah gc, linux-amd64)
# Problematic frame:
# V [libjvm.so+0xd7155e] java_lang_String::equals(oop, unsigned short const*, int)+0x6e
#

Disassembly code:

push %rbp
 mov %rsp,%rbp
 push %r15
 push %r14
 push %r13
 push %r12
 mov %rdi,%r14
 push %rbx
 mov %rsi,%r15
 sub $0x48,%rsp
 mov %edx,-0x58(%rbp)
 lea 0x142857b(%rip),%rdx # 0x7ffff7182a8c <UseCompressedClassPointers>
 mov (%rdi),%rax
 cmpb $0x0,(%rdx)
 jne 0x7ffff5d5a700 <java_lang_String::equals(oop, unsigned short const*, int)+528>
 mov 0x8(%rax),%r12
 lea 0x1464b18(%rip),%rax # 0x7ffff71bf040 <_ZN9vmClasses8_klassesE>
 mov 0x8(%rax),%rbx
 test %rbx,%rbx
 je 0x7ffff5d5a729 <java_lang_String::equals(oop, unsigned short const*, int)+569>
 cmp %r12,%rbx <<== java_string.klass == VMClasses::String_Klass()
 je 0x7ffff5d5a56d <java_lang_String::equals(oop, unsigned short const*, int)+125>
 lea 0x139bcc7(%rip),%rax # 0x7ffff70f6208 <g_assert_poison>
 lea 0xd181ea(%rip),%rcx # 0x7ffff6a72732
 lea 0xd28059(%rip),%rdx # 0x7ffff6a825a8
 lea 0xd27d2a(%rip),%rdi # 0x7ffff6a82280
  mov $0x2e9,%esi
  mov (%rax),%rax
  movb $0x58,(%rax)
  xor %eax,%eax


It looks like rax has corrupted oop